The present invention relates to packaging polymers, particularly bottles made from packaging polymer compositions, and particularly polyester polymer compositions which have an improved infrared (IR) absorption characteristic. More specifically, the present invention relates to a polyester polymer composition that includes inorganic black pigments or particles as an infrared absorbing material. The present invention envisions the use of the polyester polymer compositions to make plastic bottles with acceptable color and clarity, and with good physical properties, and with improved infrared absorbing properties.
The use of polyester compositions as a packaging material, particularly, compositions comprising polyethylene terephthalate, generally referred to as xe2x80x9cPET,xe2x80x9d in the form of films, plastic bottles and other containers is well known. Plastic bottles are used for containing pressurized fluids such as carbonated drinks, e.g., soft drinks or mineral waters, as well as for non-carbonated, non-pressurized drinks. To form plastic bottles, the polymer is extruded and then formed into chips. The chips are employed to make a bottle preform by injection molding as is well known in the industry. The preform is then reheated and blown into a mold which provides the final shape of the bottle. The blow-molding step causes biaxial orientation of the polyester composition to occur at least in the side walls and the bottom of the bottles, and to a lesser degree in the neck. The biaxial orientation provides strength to the bottle so that it can resist deformation from internal pressure during use and adequately contain the fluid over an industry standardized shelf-life.
To summarize, a conventional polyester chip based on a modified PET resin is generally shipped to plastic bottle manufacturers who injection mold the polymer to make a bottle preform. The preform must then be heated to about 105xc2x0 C. and blow-molded into a bottle shape. The rate of production of plastic bottles is usually limited by the time required to heat the preform. To reduce the energy required to heat the preform and to cause the preform to quickly achieve the desired blow-molding temperature of about 105xc2x0 C. would be particularly useful in the industry. Of course, the blow-molding temperature varies for different polyester compositions; for example, polyethylene naphthalate would require a different blow-molding temperature.
Heating a conventional polyester preform to about 105xc2x0 C. is typically achieved with commercially available quartz infrared lamps which emit in the near infrared region (NIR) as well as in the infrared region (IR) as will be more clearly explained later. The absorption of infrared radiation by PET is low because PET tends to absorb infrared radiation only at certain frequencies as will be described later. Thus, the rate of heating PET is very dependent upon the ability of the polymer resin to absorb the infrared radiation and any component within the PET composition which can improve the absorption of infrared radiation is commercially useful for bottle manufacturers.
U.S. Pat. Nos. 5,409,983, 5,419,936 and 5,529,744 to Tindale and assigned to ICI disclose a polyester composition which includes an infrared radiation absorbing material comprising suitable metals which intrinsically absorb radiation in the wavelength region of 0.5 micron to 2 microns (NIR and IR) to substantially reduce the reheat time of the polymer or bottle preform. Suitable NIR and IR absorbing metals include antimony, tin, copper, silver, gold, arsenic, cadmium, mercury, lead, palladium and platinum, and mixtures thereof. For most applications, the metals silver, gold, arsenic, cadmium, mercury, lead, palladium and platinum are either too expensive or environmentally hazardous and these metals are not particularly preferred. The preferred metals are one or more of antimony, tin or copper, antimony being particularly preferred.
U.S. Pat. Nos. 4,408,004, and 4,535,118 to Pengilly and initially assigned to Goodyear disclose a polyester having improved infrared absorbing materials contained therein. The only infrared absorbing material mentioned is carbon black including specific types such as channel black and furnace black. The carbon black has an average particle size from 10 to 500 nanometers and is used at a concentration from 0.1 to 10 parts by weight per million parts by weight of the polyester employed. This composition substantially reduces the time required to heat the preform to approximately 105xc2x0 C.
The present invention relates to a polymer resin containing inorganic black pigments or particles, the size of the inorganic pigments or particles being such that they are not readily visible to the naked eye when uniformly dispersed in the resin and present in an amount from about 3 to about 150 parts by weight per million parts (ppm) by weight of the polymer resin. Preferably, the polymer contains at least about 80% by weight polyester polymer. The preferred polymer resin is a polyester resin.
In addition, the present invention includes a method of heating either a polyester resin or a polyester bottle preform by exposing the polyester resin or polyester bottle preform to infrared radiation for a sufficient time to heat the polyester resin or polyester bottle preform to greater than ambient temperature, wherein the polyester resin or polyester bottle preform contains about 3 to about 150 ppm inorganic black pigments or particles, the particles being not readily visible to the naked eye when uniformly dispersed therein.
Further, the present invention also relates to a bottle preform which can be heated with IR heaters to the desired blow-molding temperature, and blow-molded in the form of a plastic bottle, said bottle preform being made from polyester that contains inorganic black pigments or particles, with the size of the particles being sufficiently small such that they are not readily visible to the naked eye when uniformly dispersed within the bottle preform.
The inorganic particles are present in an amount from about 3 to about 150 ppm based upon the amount of polyester resin.
The present invention also relates to a plastic bottle made from polyester that contains inorganic black pigments or particles, said particles being sufficiently small that they are not readily visible to the naked eye upon uniform distribution within the plastic bottle and are employed in an amount of about 3 to about 150 ppm based on the amount of polyester.